Rubber composition comprising a specific crumb rubber

ABSTRACT

A rubber composition is based on at least an elastomer, a reinforcing filler, a crosslinking system and a crumb rubber, in which the crumb exhibits a content of sulfur and a content of accelerator such that their sum is less than or equal to 5 parts by weight per 100 parts by weight of elastomer (phr), the said crumb exhibiting a total sulfur content of less than or equal to 4 parts by weight per 100 parts by weight of elastomer (phr) in the composition of the crumb.

The invention relates to compositions, in particular for tyres, and moreespecially to compositions comprising a crumb rubber.

This is because it is advantageous today for tyre manufacturers to findsolutions for lowering the costs of rubber compositions withoutpenalizing the performance qualities of the tyres using thesecompositions.

It is known in the state of the art that crumb rubbers can be used intyres. For example, the document US 2014/0228505 describes the use of acrumb rubber with a to size of less than 60 mesh (250 μm) incompositions for tyres.

The Applicant Companies have now shown that the distinctive compositionof the crumbs used has an impact on the properties of the compositionscomprising these crumb rubbers. In particular, the Applicant Companieshave found a means of obtaining excellent tear strength properties incompositions comprising specific crumbs.

The invention thus relates to a rubber composition based on at least anelastomer, a reinforcing filler, a crosslinking system and a crumbrubber, in which the crumb exhibits a content of sulfur and a content ofaccelerator such that their sum is less than or equal to 5 parts byweight per 100 parts by weight of elastomer (phr), the said crumbexhibiting a total sulfur content of less than or equal to 4 parts byweight per 100 parts by weight of elastomer (phr) in the composition ofthe crumb.

The invention also relates to a tyre comprising a composition as definedabove, preferably in all or part of its tread.

Preferably, the tyre according to the invention will be chosen from thetyres intended to equip a two-wheel vehicle, a passenger vehicle, oralso a “heavy-duty” vehicle (that is to say, underground, bus, off-roadvehicles, heavy road transport vehicles, such as lorries, tractors ortrailers), or also aircraft, construction equipment, heavy agriculturalvehicles or handling vehicles.

I—CONSTITUENTS OF THE COMPOSITION

The rubber compositions according to the invention are based on at leastan elastomer, a reinforcing filler, a crosslinking system and a crumbrubber, in which the crumb exhibits a content of sulfur and a content ofaccelerator such that their sum is less than or equal to 5 parts byweight per 100 parts by weight of elastomer (phr), the said crumbexhibiting a total sulfur content of less than or equal to 4 parts byweight per 100 parts by weight of elastomer (phr) in the composition ofthe crumb.

The expression “composition based on” should be understood as meaning acomposition comprising the mixture and/or the product of the in situreaction of the various base constituents used, some of theseconstituents being able to react and/or being intended to react with oneanother, at least partially, during the various phases of manufacture ofthe composition or during the subsequent curing, modifying thecomposition as it is prepared at the start. Thus, the compositions asemployed for the invention can be different in the non-crosslinked stateand in the crosslinked state.

Furthermore, the term “phr”, which is well known to a person skilled inthe art, means, within the meaning of the present patent application,part by weight per hundred parts of elastomers, within the meaning ofthe preparation of the composition before curing, that is to say, in thecase of the presence of a crumb rubber in a composition, that the term“phr” means part by weight per hundred parts of “new” elastomers, thusexcluding from the base 100 the elastomers contained in the crumbrubber. Of course, the crumb itself exhibits a rubber composition, theingredients of which can also be expressed in phr, the term “phr” inthis case denoting the amount in parts by weight per hundred parts ofelastomers, within the meaning of the distinctive composition of thecrumb.

In the present description, unless expressly indicated otherwise, allthe percentages (%) shown are percentages by weight. Furthermore, anyinterval of values denoted by the expression “between a and b”represents the range of values extending from more than a to less than b(that is to say, limits a and b excluded), whereas any interval ofvalues denoted by the expression “from a to b” means the range of valuesextending from a up to b (that is to say, including the strict limits aand b).

When reference is made to a “predominant” compound, this is understoodto mean, within the meaning of the present invention, that this compoundis predominant among the compounds of the same type in the composition,that is to say that it is the one which represents the greatest amountby weight among the compounds of the same type and in particular morethan 50%, preferably more than 75%. Thus, for example, a predominantpolymer is the polymer representing the greatest weight with respect tothe total weight of the polymers in the composition. In the same way, a“predominant” filler is the one representing the greatest weight amongthe fillers of the composition. By way of example, in a systemcomprising just one polymer, the latter is predominant within themeaning of the present invention and, in a system comprising twopolymers, the predominant polymer represents more than half of theweight of the polymers. On the contrary, a “minor” compound is acompound which does not represent the greatest fraction by weight amongthe compounds of the same type.

Within the meaning of the present invention, when reference is made to a“predominant” unit (or monomer) within one and the same compound (orpolymer), this is understood to mean that this unit (or monomer) ispredominant among the units (or monomers) forming the compound (orpolymer), that is to say that it is the one which represents thegreatest fraction by weight among the units (or monomers) forming thecompound (or polymer). Thus, for example, a resin predominantly composedof cyclopentadiene units is a resin in which the cyclopentadiene unitsrepresent the greatest amount by weight among all the units making upthe said resin. In the same way, a resin predominantly composed of unitsselected from the group consisting of cyclopentadiene,dicyclopentadiene, methylcyclopentadiene and the mixtures of these is aresin in which the sum of the units selected from the group consistingof cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and themixtures of these represents the greatest number by weight among all theunits making up the said resin. In other words, a “predominant” monomeris a monomer which represents the greatest fraction by weight in thepolymer. On the contrary, a “minor” monomer is a monomer which does notrepresent the greatest molar fraction in the polymer.

In the present patent application, when reference is made to a ratio ofthe amounts of a compound A and of a compound B, or a ratio between thecontent of a compound A and the content of a compound B, this is alwaysthe ratio in the mathematical sense of the amount of compound A to theamount of compound B.

The compounds mentioned in the description can be of fossil or biobasedorigin. In the latter case, they may partially or completely result frombiomass or be obtained from renewable starting materials resulting frombiomass. Polymers, plasticizers, fillers, and the like, are concerned inparticular.

I-1 Elastomer

The elastomer can be selected from the group consisting of dieneelastomers and the mixtures of these.

It is recalled here that elastomer (or “rubber”, the two terms beingregarded as synonymous) of the “diene” type should be understood, in aknown way, as meaning an (one or more is understood) elastomer resultingat least in part (i.e., a homopolymer or a copolymer) from dienemonomers (monomers bearing two conjugated or non-conjugatedcarbon-carbon double bonds).

Diene elastomers can be classified into two categories: “essentiallyunsaturated” or “essentially saturated”. “Essentially unsaturated” isunderstood to mean generally a diene elastomer resulting at least inpart from conjugated diene monomers having a content of units of dieneorigin (conjugated dienes) which is greater than 15% (mol %); to thus itis that diene elastomers such as butyl rubbers or copolymers of dienesand of α-olefins of EPDM type do not come within the precedingdefinition and can in particular be described as “essentially saturated”diene elastomers (low or very low content, always less than 15%, ofunits of diene origin). In the category of “essentially unsaturated”diene elastomers, “highly unsaturated” diene elastomer is understood inparticular to mean a diene elastomer having a content of units of dieneorigin (conjugated dienes) which is greater than 50%.

Given these definitions, diene elastomer capable of being used in thecompositions according to the invention is understood more particularlyto mean:

(a) any homopolymer obtained by polymerization of a conjugated dienemonomer having from 4 to 12 carbon atoms;(b) any copolymer obtained by copolymerization of one or more conjugateddienes with one another or with one or more vinylaromatic compoundshaving from 8 to 20 carbon atoms;(c) a ternary copolymer obtained by copolymerization of ethylene and ofan α-olefin having from 3 to 6 carbon atoms with a non-conjugated dienemonomer having from 6 to 12 carbon atoms, such as, for example, theelastomers obtained from ethylene and propylene with a non-conjugateddiene monomer of the abovementioned type, such as, in particular,1,4-hexadiene, ethylidenenorbornene or dicyclopentadiene;(d) a copolymer of isobutene and of isoprene (butyl rubber) and also thehalogenated versions, in particular chlorinated or brominated versions,of this type of copolymer.

Although it applies to any type of diene elastomer, a person skilled inthe art of tyres will understand that the present invention ispreferably employed with essentially unsaturated diene elastomers, inparticular of the type (a) or (b) above.

The following are suitable in particular as conjugated dienes:1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C₁-C₅alkyl)-1,3-butadienes, such as, for example, 2,3-dimethyl-1,3-butadiene,2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene or2-methyl-3-isopropyl-1,3-butadiene, aryl-1,3-butadiene, 1,3-pentadieneor 2,4-hexadiene. The following, for example, are suitable asvinylaromatic compounds: styrene, ortho-, meta- or para-methylstyrene,the “vinyltoluene” commercial mixture, para-(tert-butyl)styrene,methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene orvinylnaphthalene.

The copolymers can contain between 99% and 20% by weight of diene unitsand to between 1% and 80% by weight of vinylaromatic units. Theelastomers can have any microstructure, which depends on thepolymerization conditions used, in particular on the presence or absenceof a modifying and/or randomizing agent and on the amounts of modifyingand/or randomizing agent employed. The elastomers can, for example, beblock, random, sequential or microsequential elastomers and can beprepared in dispersion or in solution; they can be coupled and/orstar-branched or else functionalized with a coupling and/orstar-branching or functionalization agent. The term “functional group”is preferably understood here to mean a chemical group which interactswith the reinforcing filler of the composition.

Preferably, the elastomer of the composition predominantly comprises anessentially unsaturated diene elastomer. The elastomer of thecomposition is preferably selected from the group consisting ofpolybutadienes (abbreviated to BRs), synthetic polyisoprenes (IRs) ornatural polyisoprenes (NRs), butadiene copolymers, isoprene copolymersand the mixtures of these elastomers. Such copolymers of butadiene andof isoprene are more preferably respectively butadiene/styrenecopolymers (SBRs) and isoprene/styrene copolymers (SIRs).

More preferably, the predominant elastomer is selected from the groupconsisting of polybutadienes, natural or synthetic polyisoprenes and themixtures of these elastomers.

I-2 Reinforcing Filler

The composition according to the invention comprises a reinforcingfiller. Use may be made of any type of reinforcing filler known for itsabilities to reinforce a rubber composition which can be used for themanufacture of tyres, for example an organic filler, such as carbonblack, a reinforcing inorganic filler, such as silica or alumina, oralso a blend of these two types of filler.

Preferably, the content of reinforcing filler is within a rangeextending from 5 to 200 phr and preferably from 20 to 160 phr.

For the requirements of the invention, the reinforcing filler ispreferably selected from the group consisting of silicas, carbon blacksand the mixtures of these. More preferably, the reinforcing filler ispredominantly carbon black, preferably at a content within a rangeextending from 30 to 90 phr. Preferably again, the reinforcing filler ispredominantly silica, preferably at a content within a range extendingfrom 30 to 90 phr.

All carbon blacks, in particular “tyre-grade” blacks, are suitable ascarbon blacks. Mention will more particularly be made, among the latter,of the reinforcing carbon blacks of the 100, 200 or 300 series (ASTMgrades), such as, for example, the N115, N134, N234, N326, N330, N339,N347 or N375 blacks, or else, depending on the applications targeted,the blacks of higher series (for example N660, N683 or N772). The carbonblacks might, for example, be already incorporated in an isopreneelastomer in the form of a masterbatch (see, for example, ApplicationsWO 97/36724 or WO 99/16600).

Mention may be made, as examples of organic fillers other than carbonblacks, of functionalized polyvinyl organic fillers, such as describedin Applications WO-A-2006/069792, WO-A-2006/069793, WO-A-2008/003434 andWO-A-2008/003435.

The composition can comprise one type of silica or a blend of severalsilicas. The silica used can be any reinforcing silica known to a personskilled in the art, in particular any precipitated or fumed silicaexhibiting a BET specific surface and a CTAB specific surface both ofless than 450 m²/g, preferably from 30 to 400 m²/g. Mention will bemade, as highly dispersible precipitated silicas (“HDSs”), for example,of the Ultrasil 7000 and Ultrasil 7005 silicas from Evonik, the Zeosil1165MP, 1135MP and 1115MP silicas from Solvay, the Hi-Sil EZ150G silicafrom PPG, the Zeopol 8715, 8745 and 8755 silicas from Huber, treatedprecipitated silicas, such as, for example, the silicas “doped” withaluminium described in Application EP-A-0735088, or the silicas with ahigh specific surface as described in Application WO 03/16387. Thesilica preferably has a BET specific surface of between 45 and 400 m²/g,more preferably of between 60 and 300 m²/g.

These compositions can optionally also comprise, in addition to thecoupling agents, coupling activators, agents for covering the inorganicfillers or more generally processing aids capable, in a known way, byvirtue of an improvement in the dispersion of the filler in the rubbermatrix and of a lowering of the viscosity of the compositions, ofimproving their ability to be processed in the raw state, these agentsbeing, for example, hydrolysable silanes, such as alkylalkoxysilanes,polyols, fatty acids, polyethers, primary, secondary or tertiary amines,or hydroxylated or hydrolysable polyorganosiloxanes.

A person skilled in the art will understand that a reinforcing filler ofanother nature, in particular organic nature, might be used as fillerequivalent to the silica described in the present section, provided thatthis reinforcing filler is covered with a layer of silica or elsecomprises, at its surface, functional sites, in particular hydroxylsites, requiring the use of a coupling agent in order to form theconnection between the filler and the elastomer.

The physical state under which the reinforcing filler is provided is notimportant, whether it is in the form of a powder, of microbeads, ofgranules, of beads or any other appropriate densified form.

I-3 Crosslinking System

In the composition of the invention, use may be made of any type ofcrosslinking system known to a person skilled in the art for rubbercompositions.

The crosslinking system is preferably a vulcanization system, that is tosay based on sulfur (or on a sulfur-donating agent) and on a primaryvulcanization accelerator. Additional to this base vulcanization systemare various known secondary vulcanization accelerators or vulcanizationactivators, such as zinc oxide, stearic acid or equivalent compounds, orguanidine derivatives (in particular diphenylguanidine), incorporatedduring the first non-productive phase and/or during the productivephase, as are described subsequently.

The sulfur is used at a preferred content of between 0.5 and 10 phr,more preferably of between 0.5 and 5 phr, in particular between 0.5 and3 phr.

The vulcanization system of the composition according to the inventioncan also comprise one or more additional accelerators, for examplecompounds of the family of the thiurams, zinc dithiocarbamatederivatives, sulfenamides, guanidines or thiophosphates. Use mayespecially be made of any compound capable of acting as accelerator ofthe vulcanization of diene elastomers in the presence of sulfur, inparticular accelerators of the thiazoles type and also theirderivatives, accelerators of thiurams type, or zinc dithiocarbamates.These accelerators are more preferably selected from the groupconsisting of 2-mercaptobenzothiazyl disulfide (abbreviated to “MBTS”),N-cyclohexyl-2-benzothiazolesulfenamide (abbreviated to “CBS”),N,N-dicyclohexyl-2-benzothiazolesulfenamide (abbreviated to “DCBS”),N-(tert-butyl)-2-benzothiazolesulfenamide (abbreviated to “TBBS”),N-(tert-butyl)-2-benzothiazolesulfenimide (abbreviated to “TBSI”), zincdibenzyldithiocarbamate (abbreviated to “ZBEC”) and the mixtures ofthese compounds. Preferably, use is made of a primary accelerator of thesulfenamide type.

I-4 Crumb Rubber

The composition of the invention also comprises a crumb rubber(abbreviated to “crumb” in the remainder of the text).

The crumbs are presented in the form of granules, optionally put intothe form of a rubber plaque. Generally, crumb rubbers result from agrinding or from a micronization of cured rubber compositions alreadyused for a first application, for example in tyres;

they are a product of the recycling of materials. The crumbs arepreferably provided in the form of microparticles.

The term “microparticles” is understood to mean particles which exhibita size, namely their diameter in the case of spherical particles ortheir greatest dimension in the case of anisometric particles, of a fewtens of or a few hundred microns.

The crumbs are usually composed of a composition based on an elastomerand on a filler. They also usually comprise all the ingredients used inrubber compositions, such as plasticizers, antioxidants, vulcanizationadditives, and the like.

In the crumbs of use for the invention, the crosslinking system ispreferably a vulcanization system, that is to say based on sulfur (or ona sulfur-donating agent) and on a vulcanization accelerator. Use may bemade of any compound capable of acting as accelerator of thevulcanization of diene elastomers in the presence of sulfur, inparticular accelerators of the thiazoles type and also theirderivatives, accelerators of thiurams type, or zinc dithiocarbamates.These accelerators are more preferably selected from the groupconsisting of 2-mercaptobenzothiazyl disulfide (abbreviated to “MBTS”),N-cyclohexyl-2-benzothiazolesulfenamide (abbreviated to “CBS”),N,N-dicyclohexyl-2-benzothiazolesulfenamide (abbreviated to “DCBS”),N-(tert-butyl)-2-benzothiazolesulfenamide (abbreviated to “TBBS”),N-(tert-butyl)-2-benzothiazolesulfenimide (abbreviated to “TBSI”), zincdibenzyldithiocarbamate (abbreviated to “ZBEC”) and the mixtures ofthese compounds. Preferably, use is made of an accelerator of thesulfenamide type.

For the requirements of the invention, the crumb rubber exhibits a totalsulfur content of less than 4 phr, preferably of less than 3 phr, in thecomposition of the crumb. The total sulfur content in the composition ofthe crumb can be measured by elemental analysis as described below.

This is because the Applicant Companies have shown that, when the totalsulfur content in the composition of the crumb is greater than or equalto 4 phr, the composition to comprising such a crumb exhibits a reducedcohesion.

Again for the requirements of the invention, the crumb rubber exhibits acontent of sulfur and a content of accelerator such that their sum isless than or equal to 5 phr, preferably less than or equal to 4 phr, inthe composition of the crumb.

This is because the Applicant Companies have shown that, when the sum ofthe contents of sulfur and of accelerator in the composition of thecrumb is greater than or equal to 5 phr, the composition comprising sucha crumb can also exhibit a reduced cohesion.

The sulfur is used at a preferred content of between 0.5 and 3 phr, inparticular between 0.5 and 2.5 phr. The accelerator is used at apreferred content of between 0.5 and 3 phr, more preferably of between0.5 and 2 phr.

The specific crumbs comprising less than 4 phr in total of sulfur may beavailable commercially and a person skilled in the art will know how toidentify the crumbs of use for the invention, in particular by theanalysis of the sulfur content in the composition of the crumb.According to one possible embodiment, use may be made of the recyclingof tyres having a known composition, so as to make sure that thecomposition of the crumb meets the specific criteria for the invention.The crumb itself, if it is not directly purchased commercially, can beobtained according to the techniques known to a person skilled in theart of grinding or micronization.

The grinding can be carried out by various technologies, in particularcryogenic impact micronization technologies, which make it possible toobtain particles of small size on rubber materials. Commercialequipment, such as the CUM150 mill from Netzsch or the CW250 mill fromAlpine, can be used.

Preferably, the crumb of use in the invention comprises a dieneelastomer. This elastomer preferably represents at least 30% by weight,more preferably at least 40% by weight, more preferably still at least50% by weight, of the weight of the crumb, which percentage isdetermined according to Standard ASTM E1131. It is preferably selectedfrom the group consisting of polybutadienes, polyisoprenes, includingnatural rubber, butadiene copolymers and isoprene copolymers. Morepreferably, the molar content of units of diene origin (conjugateddienes) present in the diene elastomer is greater than 50%, preferablybetween 50% and 70%.

According to a preferred embodiment of the invention, the crumb containsbetween 5% and 80% by weight of filler, more preferably between 10% and75% and very preferably between 15% and 70%.

The term “filler” is understood here to mean any type of filler, whetherit is reinforcing (typically having nanometric particles, preferablywith a weight-average size of less than 500 nm, in particular between 20and 200 nm) or whether it is non-reinforcing or inert (typically havingmicrometric particles, preferably with a weight-average size of greaterthan 1 μm, for example between 2 and 200 μm). The weight-average size ofthe nanometric particles is measured in a way well known to a personskilled in the art (by way of example, according to Application WO2009/083160, section 1.1). The weight-average size of the micrometricparticles can be determined by mechanical sieving.

Mention will in particular be made, as examples of fillers known asreinforcing by a person skilled in the art, of carbon black or of areinforcing inorganic filler, such as silica or alumina in the presenceof a coupling agent, or their mixtures.

According to a preferred embodiment of the invention, the crumbcomprises, by way of filler, a reinforcing filler, in particular acarbon black or a mixture of carbon blacks.

The carbon black or the mixture of carbon blacks preferably representsmore than 50%, more preferably more than 80%, more preferably still morethan 90%, by weight, of the weight of the reinforcing filler of thecrumb. According to a more preferred embodiment, the reinforcing fillerconsists of a carbon black or of a mixture of carbon blacks.

Very preferably, the carbon black is present in the crumb at a contentranging from 20% to 40% by weight, more preferably from 25% to 35% byweight.

All carbon blacks, in particular blacks of the HAF, ISAF, SAF, FF, FEF,GPF and SRF type, conventionally used in rubber compositions for tyres(“tyre-grade” blacks) are suitable as carbon blacks.

The crumb can contain all the other usual additives which participate ina rubber composition, in particular for a tyre. Mention may be made,among these usual additives, of liquid or solid plasticizers,non-reinforcing fillers, such as chalk or kaolin, or protective agents.These additives can be found in the crumb also in the form of residue orof derivative, since they were able to react during the stages ofmanufacture of the composition or of crosslinking of the compositionfrom which the crumb results.

As regards the constituents of the crumb, it is preferable, for therequirements of the invention, for the crumb to exhibit an acetoneextract of between 3% and 30% by weight, more preferably within a rangeextending from 5% to 25% by weight.

It is also preferable for the crumb to exhibit a chloroform extract ofbetween 5% and 85% by weight, more preferably within a range extendingfrom 5% to 50% by weight.

The crumbs can be simple ground/micronized rubber materials, withoutother treatment. It is also known that these crumbs can undergo atreatment in order to modify them. This treatment can consist of achemical functionalization or devulcanization modification. It can alsobe a thermomechanical, thermochemical, biological, and the like,treatment.

According to a, preferred, first embodiment of the invention, it ispossible to use a crumb which has not undergone modification by thermaland/or mechanical and/or biological and/or chemical treatment.

According to this first embodiment, it is preferable for the crumb toexhibit an acetone extract of between 3% and 15% by weight, morepreferably within a range extending from 3% to 10% by weight. It is alsopreferable for the crumb to exhibit a chloroform extract of between 3%and 20% by weight, more preferably within a range extending from 5% to15% by weight. Preferably, the chloroform extract of the crumb rubberexhibits a weight-average molecular weight (Mw) of less than 10 000g/mol, preferably of less than 8000 g/mol.

According to the first embodiment, it is preferable for the ratio of thechloroform extract to the acetone extract, expressed as percentage byweight, to be less than 1.5.

Also preferably according to this first embodiment, the crumb exhibitsan average particle size (D50) of between 10 and 400 μm, preferablybetween 50 and 200 μm and more preferably between 70 and 200 μm.

According to a second embodiment of the invention, it is possible to usea crumb which exhibits a morphology modified by thermal and/ormechanical and/or biological and/or chemical treatment.

According to this second embodiment, it is preferable for the crumb toexhibit an acetone extract of between 5% and 20% by weight, morepreferably within a range extending from 10% to 18% by weight. It isalso preferable for the crumb to exhibit a chloroform extract of between15% and 85% by weight, more preferably within a range extending from 15%to 50% by weight. Preferably, the chloroform extract of the crumb rubberexhibits a weight-average molecular weight (Mw) of greater than 10 000g/mol, preferably of greater than 20 000 g/mol and more preferably ofgreater than 30 000 g/mol.

According to the second embodiment, it is preferable for the ratio ofthe chloroform extract to the acetone extract, expressed as percentageby weight, to be greater than or equal to 1.5, preferably greater than2.

Also preferably according to this second embodiment, the crumb exhibitsa Mooney viscosity (conventionally expressed in Mooney unit, MU) ofbetween 40 and 90, preferably between 45 and 75 and more preferablybetween 50 and 70.

The grinding can be carried out by various technologies, in particularcryogenic impact micronization technologies, which make it possible toobtain particles of small size on rubber materials. Commercial items ofequipment, such as the CUM150 mill from Netzsch or the CW250 mill fromAlpine, can be used.

Preferably, the crumb is present at a content within a range extendingfrom 5% to 40% by weight, preferably from 10% to 30% and more preferablyfrom 15% to 25%.

In a typical composition intended for the tyre, these contents by weightcorrespond to contents of 5 to 100 phr. Below 5 phr, the saving madewould not be significant enough, whereas, above 100 phr, it is possiblefor the cohesion properties of the composition to be penalized. Thus,the crumb content is preferably within a range extending from 10 to 90phr, preferentially from 15 to 90 phr, more preferentially from 20 to 80phr and very preferentially from 30 to 70 phr, for an optimumfunctioning of the invention.

I-5 Other Possible Additives

The rubber compositions in accordance with the invention optionally alsocomprise all or a portion of the usual additives generally used inelastomer compositions intended in particular for the manufacture oftreads, such as, for example, pigments, protective agents, such asantiozone waxes, chemical antiozonants or antioxidants, plasticizingagents other than those described above, anti-fatigue agents,reinforcing resins, methylene acceptors (for example phenolic novolakresin) or methylene donors (for example HMT or H3M).

The composition according to the invention can also comprise aplasticizing system. This plasticizing system can be composed of ahydrocarbon resin with a Tg of to greater than 20° C., in addition tothe specific hydrocarbon resin described above, and/or a plasticizingoil.

Of course, the compositions in accordance with the invention can be usedalone or as a blend (i.e., as a mixture) with any other rubbercomposition which can be used for the manufacture of tyres.

It is obvious that the invention relates to the rubber compositionsdescribed above both in the “raw” or non-crosslinked state (i.e., beforecuring) and in the “cured” or crosslinked, or also vulcanized, state(i.e., after crosslinking or vulcanization).

II—PREPARATION OF THE RUBBER COMPOSITIONS

The compositions are manufactured in appropriate mixers using twosuccessive preparation phases well known to a person skilled in the art:a first phase of thermomechanical working or kneading (sometimesdescribed as “non-productive” phase) at high temperature, up to amaximum temperature of between 110° C. and 200° C., preferably between130° C. and 180° C., followed by a second phase of mechanical working(sometimes described as “productive” phase) at lower temperature,typically of less than 110° C., for example between 60° C. and 100° C.,during which finishing phase the crosslinking or vulcanization system isincorporated; such phases have been described, for example, inApplications EP-A-0 501 227, EP-A-0 735 088, EP-A-0 810 258, WO00/05300or WO00/05301.

The first (non-productive) phase is preferably carried out in severalthermomechanical stages. During a first stage, the elastomers, thereinforcing fillers and the crumb (and optionally the coupling agentsand/or other ingredients, with the exception of the crosslinking system)are introduced into an appropriate mixer, such as an ordinary internalmixer, at a temperature between 20° C. and 100° C. and preferablybetween 25° C. and 100° C. After a few minutes, preferably from 0.5 to 2min, and a rise in the temperature to 90° C. to 100° C., the otheringredients (that is to say, those which remain if not all were put inat the start) are added all at once or portionwise, with the exceptionof the crosslinking system, during a compounding ranging from 20 secondsto a few minutes. The total duration of the kneading, in thisnon-productive phase, is preferably between 2 and 10 minutes at atemperature of less than or equal to 180° C. to and preferentially ofless than or equal to 170° C.

After cooling the mixture thus obtained, the crosslinking system is thenincorporated at low temperature (typically less than 100° C.), generallyin an external mixer, such as an open mill; the combined mixture is thenmixed (productive phase) for a few minutes, for example between 5 and 15min.

The final composition thus obtained is subsequently calendered, forexample in the form of a sheet or of a plaque, in particular for alaboratory characterization, or else extruded, in order to form, forexample, a rubber profiled element used in the manufacture ofsemi-finished products for tyres. These products can subsequently beused in the manufacture of tyres, according to techniques known to aperson skilled in the art, with the advantage of the invention, namelygood tack of the layers on one another before curing of the tyre.

The crosslinking (or curing) is carried out in a known way at atemperature generally of between 130° C. and 200° C., under pressure,for a sufficient time which can vary, for example, between 5 and 90 min,as a function in particular of the curing temperature, of thecrosslinking system adopted, of the kinetics of crosslinking of thecomposition under consideration or else of the size of the tyre.

The examples which follow illustrate the invention without, however,limiting it.

III—IMPLEMENTATIONAL EXAMPLES OF THE INVENTION III-1 Characterization ofthe Crumb Rubbers and of the Rubber Compositions of the Examples

In the examples, the crumb rubbers are characterized as indicated below.

Measurement of the Size of the Particles:

The size of the particles (in particular the D50) can be measured by alaser particle size analyser of the Mastersizer 3000 type from Malvern.The measurement is carried out by the liquid route, diluted in alcoholafter an ultrasound pretreatment for 1 min in order to guarantee thedispersion of the particles. The measurement is carried out inaccordance with Standard ISO-13320-1.

Measurement of the Acetone Extract:

The acetone extract content is measured according to Standard ISO1407 bymeans of an extractor of Soxhlet type.

A test sample (between 500 mg and 5 g) is introduced into an extractionchamber and then placed in the extractor tube of the Soxhlet. A volumeof acetone equal to two or three times the volume of the extractor tubeis placed in the collector of the Soxhlet. The Soxhlet is subsequentlyassembled and then heated for 16 h.

The sample is weighed after extraction. The acetone extract contentcorresponds to the loss in weight of the sample during the extraction,with respect to its initial weight.

Measurement of the Chloroform Extract:

The chloroform extract content is measured according to Standard ISO1407by means of an extractor of Soxhlet type.

A test sample (between 500 mg and 5 g) is introduced into an extractionchamber and then placed in the extractor tube of the Soxhlet. A volumeof chloroform equal to two or three times the volume of the extractortube is placed in the collector of the Soxhlet. The Soxhlet issubsequently assembled and then heated for 16 h.

The sample is weighed after extraction. The chloroform extract contentcorresponds to the loss in weight of the sample during the extraction,with respect to its initial weight.

Measurement of the Average Molecular Weights of the Chloroform Extract:

The molecular weights are determined by size exclusion chromatography,according to a Moore calibration and according to Standard ISO16014.

The weight-average molecular weight (Mw) of the chloroform extract ismeasured by size exclusion chromatography (SEC) with a refractive index(RI) detector. The system is composed of an Alliance 2695 line fromWaters, of a column oven from Waters and also of an RI 410 detector fromWaters. The set of columns used is composed of two PL Gel Mixed Dcolumns (300×7.5 mm 5 μm), followed by two PL Gel Mixed E columns(300×7.5 mm 3 μm) from Agilent. These columns are placed in a columnoven thermostatically controlled at 35° C. The mobile phase used isnon-antioxidized tetrahydrofuran. The flow rate of the mobile phase is 1ml/min. The RI detector is also thermostatically controlled at 35° C.

The chloroform extract is dried under a nitrogen stream. The dry extractis subsequently taken up at 1 g/I in non-antioxidized tetrahydrofuran at250 ppm with stirring for 2 hours. The solution obtained is filteredusing a syringe and a single-use 0.45 μm PTFE syringe filter. 100 μl ofthe filtered solution are injected into the conditioned chromatographicsystem at 1 ml/min and 35° C.

The Mw results are provided by integration of the chromatographic peaksdetected by the RI detector above a value of 2000 g/mol. The Mw iscalculated from a calibration carried out using polystyrene standards.

Measurement of the Mooney Viscosity (or Mooney Plasticity)

Use is made of an oscillating consistometer as described in FrenchStandard NF T 43-005 (1991). The Mooney plasticity measurement iscarried out according to the following principle: the composition in theraw state (i.e., before curing) is moulded in a cylindrical chamberheated to 100° C. After preheating for one minute, the rotor rotateswithin the test specimen at 2 revolutions/minute and the working torquefor maintaining this movement is measured after rotating for 4 minutes.The Mooney plasticity (ML 1+4) is expressed in “Mooney unit” (MU, with 1MU=0.83 newton·metre). The lower the Mooney value, the lower theviscosity before curing and the better the processability of thecomposition.

Measurement of the Fraction by Weight of Carbon Black:

The fraction by weight of carbon black is measured by athermogravimetric analysis (TGA) according to Standard NF T-46-07, on anappliance from Mettler Toledo, model “TGA/DSC1”. Approximately 20 g ofsample are introduced into the thermal analyser, then subjected to athermal program from 25 to 600° C. under an inert atmosphere(pyrolysable phase) and then from 400 to 750° C. under an oxidizingatmosphere (oxidizable phase). The weight of the sample is continuouslymeasured throughout the thermal programme. The black content correspondsto the loss of weight measured during the oxidizable phase, with respectto the initial weight of sample.

Measurement of the Total Sulfur Content in the Composition of the Crumb:

The sulfur content in the composition of the crumb is measured byelemental analysis, using the Thermo Scientific Flash 2000microanalyser. The analysis comprises a stage of combustion of thesample and then a stage of separation of the compounds formed.

Approximately 1 mg of sample is introduced into the microanalyser, whereit is subjected to a flash combustion of 1000° C. under oxygen. Thegases formed are then oxidized by virtue of the excess oxygen and of atungstic anhydride catalyst. A stage of reduction by passing over coppersubsequently makes it possible to trap the excess oxygen and to reducethe nitrogen oxides to give N₂ and also the sulfites to give sulfur todioxide SO₂. The water is trapped and the compounds N₂, CO₂ and SO₂formed are subsequently separated on a chromatographic column and thendetected by a katharometer. The total sulfur is quantified bymeasurement of the area of the SO₂ peak, after calibration withstandards.

In the examples, the rubber compositions are characterized, beforeand/or after curing, as indicated below.

Measurement of the Elongation at Break at 23° C. and at 100° C.:

The measurement is carried out by tensile tests, which make it possibleto determine the elasticity stresses and the properties at break. Unlessotherwise indicated, they are carried out in accordance with FrenchStandard NF T 46-002 of September 1988. All these tensile measurementsare carried out under the standard conditions of temperature (23±2° C.)or at 100° C., if appropriate, and of hygrometry (50±10% relativehumidity). The elongations at break (in %) are measured in particular.

The results are given in base 100 in order to make the results easier toread and understand; that is to say that the value 100 is arbitrarilyassigned to the best control, in order to subsequently compare thevalues of the various solutions tested. In this way, a lower valuerepresents a decrease in tear strength performance (that is to say, adecrease in the elongation at break), whereas a higher value representsa better performance.

III-2 Preparation of the Crumbs

For the implementational examples, the crumbs used result from thegrinding of a heavy-duty vehicle tyre tread composition as presented inTable 1 below. The grinding is carried out on an item of equipmentCUM150 from Netzsch using pin diameters of 3 mm and a rotational speedof the mill of 15 000 rpm. The material flow rate is of the order of 50kg/h and the facility is cooled in order to guarantee a gas temperatureat the outlet of the mill of −60° C.

TABLE 1 Crumb composition P1 P2 NR (1) 100 100 Carbon black (2) 57 57Antioxidant (3) 1.5 1.5 Stearic acid (4) 2 2 Zinc oxide (5) 3 3Accelerator (6) 2 1.5 Sulfur 5 1.5 Sulfur + accelerator content 7 3Total S content (7) 5.6 2.1 Acetone extract 4.6% 4.6% Chloroform extract6.3% 6.3% Mw (Chloroform extract) 7000 g/mol 7000 g/mol D50 155 μm 155μm (1) NR: Natural rubber (2) Carbon black, ASTM N234 grade (3)N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (Santoflex 6-PPD)from Flexsys (4) Stearin, Pristerene 4931 from Uniqema (5) Zinc oxide,industrial grade - Umicore (6) N-Cyclohexyl-2-benzothiazolesulfenamide(Santocure CBS from Flexsys) (7) The total sulfur in the compositionvery predominantly originates from the sulfur added in the crosslinkingsystem but also from the sulfur present in other ingredients of thecomposition. An amount of the order of 0.5% of sulfur is present in thecarbon black. A small amount (0.1%) of sulfur is also contributed by theaccelerator CBS.

III-3 Rubber Compositions

The compositions are manufactured with introduction of all of theconstituents onto an internal mixer, with the exception of thevulcanization system. The vulcanization agents (sulfur and accelerator)are introduced onto an external mixer at low temperature (theconstituent rollers of the mixer being at approximately 30° C.). Thecrumbs can be introduced into the internal or external mixer.

The object of the examples presented in Table 2 is to compare thedifferent rubber properties of the control compositions (C1 and C2) withthe properties of the compositions in accordance with the invention (I1and I2). The properties measured, before and after curing, are presentedin Table 3.

TABLE 2 C1 I1 C2 I2 NR (1) 80 80 100 100 BR (2) 20 20 0 0 Carbon black(3) 48 48 48 48 Crumb P1 40 0 40 0 Crumb P2 0 40 0 40 Antioxidant (4) 33 3 3 Stearic acid (5) 2 2 2 2 Zinc oxide (6) 3 3 3 3 Accelerator (7) 11 1 1 Sulfur 1.5 1.5 1.5 1.5 (1) NR: Natural rubber (2) BR:polybutadiene, CB24 from Lanxess; 96% of cis-1,4; Tg = −107° C. (3)Carbon black, ASTM N234 grade (4)N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (Santoflex 6-PPD)from Flexsys (5) Stearin, Pristerene 4931 from Uniqema (6) Zinc oxide,industrial grade - Umicore (7) N-Cyclohexyl-2-benzothiazolesulfenamide(Santocure CBS from Flexsys)

TABLE 3 C1 I1 C2 I2 Elongation at break at 100° C. (base 100) 100 136100 140 Elongation at break at 23° C. (base 100) 100 118 100 122

In comparison with the control composition, it is noted that thecomposition I in accordance with the invention makes it possible toimprove the tear strength, as shown by the measurements of elongation atbreak at 23° C. and at 100° C.

1.-29. (canceled)
 30. A rubber composition based on at least anelastomer, a reinforcing filler, a crosslinking system, and a crumbrubber, wherein the crumb rubber exhibits a content of sulfur and acontent of accelerator such that a sum of the contents is less than orequal to 5 parts by weight per 100 parts by weight of elastomer (phr),and wherein the crumb rubber exhibits a total sulfur content of lessthan or equal to 4 parts by weight per 100 parts by weight of elastomer(phr) in the composition of the crumb rubber.
 31. The rubber compositionaccording to claim 30, wherein the crumb rubber exhibits a total sulfurcontent of less than or equal to 3 phr in the composition of the crumbrubber.
 32. The rubber composition according to claim 30, wherein thecrumb rubber exhibits a content of sulfur and a content of acceleratorsuch that the sum of the contents is less than or equal to 4 phr in thecomposition of the crumb rubber.
 33. The rubber composition according toclaim 30, wherein the crumb rubber is present at a content ranging from5% to 40% by weight.
 34. The rubber composition according to claim 30,wherein the crumb rubber is present at a content ranging from 5 to 100phr.
 35. The rubber composition according to claim 30, wherein the crumbrubber exhibits an acetone extract of between 3% and 30% by weight. 36.The rubber composition according to claim 30, wherein the crumb rubberexhibits a chloroform extract of between 5% and 85% by weight.
 37. Therubber composition according to claim 30, wherein the crumb rubber hasnot undergone modification by a method selected from the groupconsisting of thermal, mechanical, biological, and chemical treatmentsand combinations thereof.
 38. The rubber composition according to claim37, wherein the crumb rubber exhibits an acetone extract of between 3%and 15% by weight.
 39. The rubber composition according to claim 37,wherein the crumb rubber exhibits a chloroform extract of between 3% and20% by weight.
 40. The rubber composition according to claim 37, whereinthe crumb rubber exhibits a ratio of a chloroform extract to an acetoneextract, expressed as percentage by weight, of less than 1.5.
 41. Therubber composition according to claim 37, wherein the crumb rubberexhibits a chloroform extract, the weight-average molecular weight ofwhich is less than 10,000 g/mol.
 42. The rubber composition according toclaim 37, wherein the crumb rubber exhibits an average particle size D50of between 10 and 400 μm.
 43. The rubber composition according to claim30, wherein the crumb rubber exhibits a morphology modified by a methodselected from the group consisting of thermal, mechanical, biological,and chemical treatments and combinations thereof.
 44. The rubbercomposition according to claim 43, wherein the crumb rubber exhibits anacetone extract of between 5% and 20% by weight.
 45. The rubbercomposition according to claim 43, wherein the crumb rubber exhibits achloroform extract of between 15% and 85% by weight.
 46. The rubbercomposition according to claim 43, wherein the crumb rubber exhibits aratio of a chloroform extract to an acetone extract, expressed aspercentage by weight, of greater than or equal to 1.5.
 47. The rubbercomposition according to claim 43, wherein the crumb rubber exhibits achloroform extract, the weight-average molecular weight of which isgreater than 10,000 g/mol.
 48. The rubber composition according to claim43, wherein the crumb rubber exhibits a Mooney viscosity of between 40and
 90. 49. The rubber composition according to claim 30, wherein thecrumb rubber exhibits a fraction by weight of carbon black ranging from20% to 40%.
 50. The rubber composition according to claim 30, whereinthe elastomer predominantly comprises an elastomer selected from thegroup consisting of essentially unsaturated diene elastomers.
 51. Therubber composition according to claim 50, wherein the predominantelastomer is selected from the group consisting of polybutadienes,polyisoprenes, butadiene copolymers, isoprene copolymers and mixturesthereof.
 52. The rubber composition according to claim 51, wherein thepredominant elastomer is selected from the group consisting ofpolybutadienes, polyisoprenes and mixtures thereof.
 53. The rubbercomposition according to claim 30, wherein the reinforcing filler isselected from the group consisting of silicas, carbon blacks andmixtures thereof.
 54. The rubber composition according to claim 30,wherein a content of reinforcing filler is within a range extending from5 to 200 phr.
 55. The rubber composition according to claim 30, whereina predominant reinforcing filler is carbon black at a content within arange extending from 30 to 90 phr.
 56. The rubber composition accordingto claim 30, wherein a predominant reinforcing filler is silica at acontent within a range extending from 30 to 90 phr.
 57. A tirecomprising the rubber composition according to claim
 30. 58. The tireaccording to claim 57, wherein the rubber composition constitutes all orpart of a tread of the tire.